1. Field of the Invention
This invention relates to magnetic recording disk drives, and more particularly to disk drives that have a fly-height sensor for sensing head-disk spacing, including head-disk contact.
2. Description of the Related Art
Magnetic recording hard disk drives use a read/write transducer or head mounted on a head carrier for reading and/or writing data to the disk. The head carrier is typically an air-bearing slider attached to an actuator arm by a suspension and positioned very close to the disk surface by the suspension. There are typically a stack of disks in the disk drive with a slider-suspension assembly associated with each disk surface in the stack.
The separation or spacing between the head and the disk surface is called the fly-height. The slider has a disk-facing air-bearing surface (ABS) that causes the slider to ride on a cushion or bearing of air generated by rotation of the disk. The slider is attached to a flexure on the suspension and the suspension includes a load beam that applies a load force to the slider to counteract the air-bearing force while permitting the slider to “pitch” and “roll”. The flying dynamics of the slider and thus the fly-height are influenced by factors such as the rotation speed of the disk, the aerodynamic shape of the slider's ABS, the load force applied to the slider by the suspension, and the pitch and roll torques applied to the slider by the suspension.
Disk drives may use a fly-height sensor, such as an electrical resistor near the ABS, to monitor the fly-height, and a fly-height actuator for changing the fly-height in response to the output of the fly-height sensor. One type of fly-height actuator is a thermal actuator with an electrically-resistive heater located on the slider near the head. When current is applied to the heater the heater expands and causes the head to expand and thus move closer to the disk surface. The fly-height can thus be monitored and actively controlled during writing. Additionally, writing can be inhibited if the fly-height sensor detects head-disk contact or near contact.
However, the use of a fly-height sensor requires a separate electrical lead on the flex cable that connects the electronics module located on the actuator arm, called the arm electronics (AE) module, and the channel electronics module located on a printed circuit card fixed relative to the disk drive housing or base. This separate lead also requires additional input/output (I/O) pins on these two modules.
Thus what is needed is disk drive with a fly-height sensor that does not require a separate lead on the flex cable and the associated increased number of I/O pins.